This application claims a benefit of priority under 35 USC section 119 based on European Patent Application No. 92 115 511.5 filed Sep. 10, 1992, the entire contents of which are hereby expressly incorporated by reference into the present application.
Within this application several publications are referenced, and the disclosures of these publications in their entireties are hereby expressly incorporated by reference into this application.
With the ordinance planned by the Federal Government on the avoidance, reduction and utilization of used electrical appliance refuse and electronics refuse (Electronic Scrap Ordinance) the reprocessing and utilization of picture tubes of television sets and computers has been dealt with in various ways. The major portion, in terms of weight, of this are the picture tubes which are, in most cases, prepared from different sorts of glass, since only smaller picture tubes are occasionally made in one piece only, that is, without any joint of the screen and the cone. The majority of such picture tubes, that is, cathode ray picture tubes, consist of three parts, that is, the screen which, when applied in accordance with the intended use, faces the viewer; the cone connected with the screen; and the neck, these three parts consisting, in detail, of different glass types. For instance, generally, the screen, or the tub shaped front part of the picture tube, is prepared from a specially designed glass type, which must exhibit high mechanical strength, be free from bubbles, because these would to a very great extent interfere with the picture written on the fluorescent screen, and, in addition, must be capable of absorbing the soft X-radiation created at the occurrence of the electron beams, and of keeping this radiation safely away from the viewer. Lead-containing glass types are not suitable for this purpose, since they change to brown color, when being bombarded with electron beams. The screen therefore generally consists of a barium-containing glass. The cone is generally fabricated from a lead-containing glass, whilst the neck is prepared from a glass enabling good lead-through of the metal parts. The picture tubes contain, on the inside of the screen, a fluorescent material; in the case of color picture tubes, fluorescent materials in the three requisite colors are present, which, combined with a shadow mask disposed in the area of the screen, enable the creation of a color picture.
It has already been known that picture tubes of this kind can be crushed by means of a shredder, the metal parts can be separated, the fluorescent materials can be flushed out, and the comminuted glass residues can be deposited on dumps.
As it must be expected that, in the Federal Republic of Germany, almost 5 million picture tubes from television sets and computer monitors will be discarded and scrapped each year, there is a strong need to recover the valuable components, in particular, the glass, of those picture tubes.
Now, in order to attain optimal and high-grade utilization, it is necessary, that one should obtain carefully sorted glass materials, which can only be accomplished by disintegrating the picture tubes in such fashion that mixing of the glass materials, especially mixing of the glass of the screen with that of the cone, is avoided.
Separating the neck is relatively easy. After the picture tube has been aerated, and after the metal parts contained in the neck have been removed, the neck can be removed by being knocked off mechanically, fused off, given a cut with a saw and broken off, or by being burst off. Due to the small portion of glass contained in the neck, an economical separating procedure should be given preference here.
What is more essential is the separation of the screen and the cone, since these two parts of the picture tube comprise the major glass portion.
Attempts have already been made to strike the cone material off the screen by means of a resonator rod or a hammer-shaped device. By this, however, a neat separation of the different glass types is often impossible in that the picture tubes often burst and fall to pieces in an undesirable manner.
Separating the cone from the screen by blasting it off is another possibility. This can be effected by means of an electrically heated flattened wire or round wire, by on-spraying a material which is ignited and burns with a lot of heat being developed, by applying a wick soaked in an appropriate combustible liquid and lighting the wick, as well as by heating with an annular burner run with a gas/oxygen mixture. These methods not only are laborious but often fail to result in a clean separation of the cone and the screen, since the glass material, due to the high thickness, displays considerable stresses which often cause breaking of the picture tube and, thus, preclude a reproducible separation of the glass materials.
Another possibility resides in separating the cone and the screen of the picture tube by cutting with a diamond saw, whereby, advantageously, the joint of the cone and the screen is cut through with two saws from both sides simultaneously. This method is also laborious and costly, and, therefore, cannot be satisfactory either.
From DE-A-37 26 795 there is known a method of opening an evacuated electron tube having an electrode which is highly sensitive to impurities, in particular the photocathode of an image intensifier tube, which method comprises the steps of heating the soldered seam of the evacuated electron tube in an evacuated chamber to at least the fusing temperature of the solder and then causing opening of the soldering gap by means of a mechanical impulse. In this, the tube can be arranged in the vacuum chamber in such a way that the two tube parts forming the soldered seam move away from one another by a predetermined distance under the influence of the mechanical impulse and gravity, so that the suspended part of the vacuum jacket of the tube will fall on the support disposed at a lower distance therebelow. The electron tubes in question are special image intensifier tubes comprising a photocathode and a fluorescent screen as well as, optionally, in addition, a four-channel secondary electron multiplier; in the case of these there is a considerable need to recover the complex, or also faulty, electrons undestroyed. These electron tubes have an annular or disk-shaped soldered seam which connects the parts of the vacuum jacket and consists of indium, that is, a metallic solder which melts at 157.degree. C. and, thus, at much lower temperatures than the glass solders conventionally employed in the manufacture of cathode ray tubes.
From Patent Abstracts of Japan. Vol. 9. No. 123 (1985) (JP-A 60 10 545) it is already known that picture tubes can be recovered in that the picture tube is immersed in nitric acid in order to decompose and remove the glass solder area at the joint between the screen and the cone, whereupon these two parts can be separated then by on-spraying hot water.
Lastly. U.S. Pat. No. 4,176,891 describes a method of reprocessing picture tubes, which also comprises the steps of cauterizing the outer region of the glass solder and subsequently bursting the picture tube at the joint by applying a thermal shock.
The latter method cannot be satisfactory in particular on account of the use of acids, since the acids have to be collected and reused.
Further, it has been found that the glass of picture tubes, in particular of television picture tubes, develops stresses, and becomes more brittle, in the course of its use, under the influence of the cathode ray and the different temperatures which occur, so that the glasses, when exposed to the action of mechanical forces, are very likely to break, and form long cracks, in an undesirable manner, so that irregular glass fragments will result, processing of which is not only difficult but also hazardous to the operating personnel on account of the sharp broken edges.